The exploit works by infecting a user when they visit a Blackhole-infected site, and their browser runs the JavaScript code, usually via a hidden iframe. If the location or URL for the malicious iframe changes or is taken down, all of the compromised sites will have to be updated to point to this new location, making it hard for the attackers. To deal with this, the Blackhole JavaScript code on compromised sites now dynamically generates pseudo-random domains, based on the date and other information, and then creates an iframe pointing to the generated domain